Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$170.55	9.796%	$187.2571	$187.26	$187.25	$187.30
Purchase #2	$79.87	10.303%	$88.099	$88.10	$88.10	$88.10
Purchase #3	$110.33	11.478%	$122.9937	$122.99	$123.00	$123.00
Purchase #4	$159.37	8.306%	$172.6073	$172.61	$172.60	$172.60
Purchase #5	$100.30	11.240%	$111.5737	$111.57	$111.55	$111.60
Purchase #6	$18.43	9.705%	$20.2186	$20.22	$20.20	$20.20
Purchase #7	$27.41	7.824%	$29.5546	$29.55	$29.55	$29.60
7 purchase totals =	$666.26		$732.3040	$732.30	$732.25	$732.40